Displacer assembly for closed cycle engines and stirling cycle refrigerators



July 30, 1968 K. w. COWANS 3,394,542

DISPLACER ASSEMBLY FOR CLOSED CYCLE ENGINES AND STIRLING CYCLE REFRIGERATORS Filed Sept. 15, 196'? a 20 i za .Z.

Arron aw United States Patent 3,394,542 DISPLACER ASSEMBLY FOR CLOSED CY- CLE ENGINES AND STIRLING CYCLE REFRIGERATORS Kenneth W. Cowans, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Sept. 15, 1967, Ser. No. 668,112 4 Claims. (Cl. 69-24) ABSTRACT 0F THE DISCLOSURE A hollow light-weight displacer or piston arrangement is disclosed for use in closed cycle reciprocating engines or Stirling cycle refrigerators wherein the operating cycle involves wide range pressure variation. The hollow displacer incorporates a one-way inlet check valve to allow maximum ambient pressure to bleed into the closed displacer chamber. A regulator valve is also provided to oifer selective communication between the displacer chamber and ambient so that the pressure Within the chamber is always equal to or greater than ambient pressure but never greater than a fixed design value.

The invention relates to a displacer assembly for use in closed cycle reciprocating engines or closed Stirling cycle refrigerating devices.

In both closed cycle reciprocating thermal engines and Stirling cycle refrigerators a closed system is involved which cycles a thermodynamic fluid back and forth between a hot chamber and an expansion chamber. During cyclic action ambient pressure varies considerably. Heretofore, displacer or piston units were either completely solid or employed heavy reinforcement in order to resist the variation in ambient pressure. An example of the type of device here under consideration is shown in my copending application, Ser. No. 658,304, filed May 18, 1967, and entitled Heat Powered Engine.

The present invention achieves improved operating efficiencies by employing a displacer that is of hollow light-weight construction coupled with a unique valving arrangement which maintains a pressure condition within the hollow displacer equal to or above ambient. Thus, the advantages of light-weight structure are available without the attendant possibility of displacer collapse or distortion because of the cyclic variation in ambient pressure.

Specifically, the hollow displacer is provided with a one-way inlet check valve which will bleed existent ambient pressure to the internal chamber of the displacer Whenever ambient pressure exceeds the pressure within the chamber.

To avoid distortion of the displacer due to an excessive pressure internally thereof, especially during the low pressure aspects of the closed cycle, the dis-placer assembly incorporates a regulator valve to bleed internal chamber pressure to ambient in the event the ambient pressure condition falls below a determined delta increment existent within the displacer chamber. Specifically, the regulator valve incorporates a one-way check valve normally held in closed position by ambient pressure coupled with a spring to supplement the closed position bias. Thus, pressure within the displacer chamber is always equal to or greater only by a determined design increment than the pressure level at ambient.

These and other advantages of the invention will become apparent in the course of the following description and from an examination of the related drawings wherein:

FIGURE 1 is a vertical, sectional, partially elevational view of a displacer assembly incorporating the invention; and

FIG. 2 is a schematic arrangement illustrating the operation of the valves associated with the displacer structure of FIG.v 1.

As earlier noted and as specifically described in said referenced patent application, displacer assemblies of the type here under consideration are used in closed cycle external combustion engines and closed cycle refrigerators. This thermodynamic cycle involves a substantial variation in ambient pressure condition as the cycle is completed. Because of this pressure variation prior art engines utilize displacer or piston structure which were either solid or structurally reinforced to prevent displacer collapse and distortion. The addition of this extra Weight materially affected the efiiciency at which the engine or refrigerator could operate.

Directing attention to FIG. 1, there will be seen a displacer indicated generally at 10 normally disposed within cylinder 11. The assembly comprises a thin cylindrical shell 12 having a thin forward wall 14 and a heavier Wall 16. The displacer 10 is hollow and defines internally thereof a cavity or chamber 18. It will be apparent that the displacer disclosed is extremely light weight, thereby reducing to a minimum the Work necessary to move the displacer through its reciprocating cycle in cylinder 11.

In the Wall 16 a one-way check valve 22 is provided which is normally biased to a closed position via spring M. As the ambient pressure within cylinder 11 rises, said pressure induces the opening of valve 22 accommodating pressure transfer to the chamber 18 of the displacer 10. Thus, at the maximum pressure condition within the cycle, the pressure externally of the displacer and the pressure internally of the displacer will approximately equalize.

At other points in the thermodynamic cycle, pressure within the cylinder 20 decreases to a minimum as described in the referenced patent application. In order to prevent excessively high pressure existing within the chamber 18 which could distort the displacer 10, a pressure regulator assembly indicated generally at 25 is provided. The regulator assembly 25 comprises a port 26 and a valve head 28 normally biased to close at port 2 6. Coiled spring 30 is provided surrounding valve stem 32 and biases head 28 to closed position. Drilled hole 33 admits ambient pressure to cavity 35, said pressure also biasing head 28 to closed position. A threaded nut 37 provides means to adjust the compressive force of spring 30. It will thus be apparent that the valve 24 is biased to closed condition as illustrated in FIG. 1 in response to the combined pressure efiect of spring 30 and the external pressure existing in the cylinder 20 distributed against valve head 28.

Directing attention to FIG. 2, the displacer :10 is here indicated schematically at 10a and check valve 22 is shown schematically at 2211. Regulating valve 24 is shown schematically at 24a.

The symbol p represents ambient pressure whereas the symbol p represents the pressure within the cavity 18 of displacer 10a. Check valve 22a is regulated to accommodate pressure bleed to the displacer 10a whenever p is greater than p It will thus be apparent that the maximum pressure p at any time existing during the cycle will be bled internally of the displacer 10a when that high pressure aspect of the cycle is reached. This maximum pressure is normally maintained within the displacer chamber throughout the operation cycle. Tl 1'e regulator valve 241:, as earlier noted, is normally biased to closed condition as a result of combined p pressure plus the biasing effect of spring 30 which is here identified as 12,. In the preferred mode of operation, the biasing force of spring 30 is adjusted by nut 37 so that valve head 28 will only open port 26 when a determined design pressure differential exists between chamber 18 and ambient. This ditferential is below that which would result in distortion of displacer 10.

With the cyclic pressure variation of the ambient condition as illustrated in the referenced patent application, it will be apparent that the pressure internally of the displacer 10 will continuously vary and be maintained at a condition wherein its internal pressure is approximately equal to or greater (within design value) than the continuously varying ambient pressure condition surrounding said displacer 10. As a result of this novel valving and bleeding arrangement, a displacer structure that is extremely light weight may be employed, thus contributing importantly to the overall efficiency of the unit.

The invention as disclosed is by way of illustration and not limitation and may be modified in many respects all within the scope of the appended claims.

What is claimed is:

1. In a displacer assembly for use in a closed cycle device,

a fixed volume hollow displacer element adapted for reciprocation within a cylinder of said device,

said device employing a closed thermodynamic cycle having a wide pressure variation during cyclic operation,

a first one-way check valve establishing communication between a chamber internally of the displacer and the cylinder to accommodate entrance into said chamber of substantially the maximum pressure level existent during said cycle,

and regulating means adapted to establish communication between the chamber and the cylinder and to accommodate pressure bleed from the chamber when the pressure diiferential between the chamber and ambient rises to a determined level.

2. A displacer assembly according to claim 1,

wherein said regulator valve comprises a valve head operatively associated with an escape port,

and means to normally bias said valve head to port closed position.

3. A displacer assembly according to claim 2,

wherein said last-mentioned means comprises spring means compressively engaging the valve head and biasing same to port closed condition,

said valve head having the surface thereon exposed to ambient pressure condition whereby said pressur normally biases said head to port closed condition.

4. A displacer assembly according to claim 3,

and including means to adjust the compressive biasing force of said spring.

References Cited UNITED STATES PATENTS l/l879 Patterson 91--422 X 12/ 1909 Hubbard 60-24 

